1. Field of the Invention
The present invention relates to an orbiting vane compressor, and, more particularly, to a back pressure apparatus for orbiting vane compressors that is capable of reducing excessive axial force applied to an orbiting vane due to high-pressure refrigerant gas introduced to the lower surface of a vane plate of the orbiting vane.
2. Description of the Related Art
Referring to FIG. 1, there is illustrated a conventional orbiting vane compressor. As shown in FIG. 1, a drive unit D and a compression unit P are mounted in a shell 1 while the drive unit D and the compression unit P are hermetically sealed. The drive unit D and the compression unit P are connected to each other via a vertical crankshaft 8, the upper and lower ends of which are rotatably supported by a main frame 6 and a subsidiary frame 7, respectively, such that power from the drive unit D is transmitted to the compression unit P through the crankshaft 8.
The drive unit D comprises: a stator 2 fixedly disposed between the main frame 6 and the subsidiary frame 7; and a rotor 3 disposed in the stator 2 for rotating the crankshaft 8, which vertically extends through the rotor 3, when electric current is supplied to the rotor 3. The rotor 3 is provided at the top and bottom parts thereof with balance weights 3a, which are disposed symmetrically to each other for preventing the crankshaft 8 from being rotated in an unbalanced state due to a crank pin 81.
The compression unit P comprises an orbiting vane 5 having a boss 55 formed at the upper part thereof. The crank pin 81 is fixedly fitted in the boss 55 of the orbiting vane 5. As the orbiting vane 5 performs an orbiting movement in a cylinder 4, refrigerant gas introduced into the cylinder 4 is compressed. The cylinder 4 comprises an inner ring 41 integrally formed at the upper part thereof while being protruded downward. The orbiting vane 5 comprises a circular vane 51 formed at the upper part thereof while being protruded upward. The circular vane 51 performs an orbiting movement in an annular space 42 defined between the inner ring 41 and the inner wall of the cylinder 4. Through the orbiting movement of the circular vane 51, inner and outer compression chambers are formed at the inside and the outside of the circular vane 51, respectively. Refrigerant gases compressed in the inner and outer compression chambers are discharged out of the cylinder 4 through inner and outer outlet ports 44 and 44a formed at the upper part of the cylinder 4, respectively.
Between the main frame 6 and the orbiting vane 5 is disposed an Oldham's ring 9 for preventing rotation of the orbiting vane 5. Through the crankshaft 8 is longitudinally formed an oil supplying channel 82 for allowing oil to be supplied to the compression unit P therethrough when an oil pump 83 mounted at the lower end of the crankshaft 8 is operated.
Unexplained reference numeral 1a indicates an inlet tube, 1b a high-pressure chamber, and 1c an outlet tube.
FIG. 2 is an exploded perspective view illustrating main components of the conventional orbiting vane compressor shown in FIG. 1.
In the compression unit P, as shown in FIG. 2, the orbiting vane 5, which is connected to the crankshaft 8, is disposed on the upper end of the main frame 6, which rotatably supports the upper part of the crankshaft 8. The cylinder 4, which is attached to the main frame 6, is disposed above the orbiting vane 5. The cylinder 4 is provided at a predetermined position of the circumferential part thereof with an inlet port 43. The inner and outer outlet ports 44 and 44a are formed at predetermined positions of the upper end of the cylinder 4.
The crank pin 81 of the crankshaft 8 is fixedly fitted in the boss 55, which is formed at the upper part of a vane plate 50 of the orbiting vane 5. At a predetermined position of the circumferential part of the circular vane 51 of the orbiting vane 5 is formed a through-hole 52 for allowing refrigerant gas introduced through the inlet port 43 of the cylinder 4 to be guided into the circular vane 51 therethrough. At another predetermined position of the circumferential part of the circular vane 51 of the orbiting vane 5, which is adjacent to the position where the through-hole 52 is disposed, is formed an opening 53. A slider 54 is disposed in the opening 53.
FIG. 3 is a plan view, in section, illustrating the operation of the conventional orbiting vane compressor.
When the orbiting vane 5 of the compression unit P is driven by power transmitted to the compression unit P from the drive unit D through the crankshaft 8 (See FIG. 1), the circular vane 51 of the orbiting vane 5 disposed in the annular space 42 of the cylinder 4 performs an orbiting movement in the annular space 42 of the cylinder 4, as indicated by arrows, to compress refrigerant gas introduced into the annular space 42 through the inlet port 43.
At the initial orbiting position of the orbiting vane 5 of the compression unit P (i.e., the 0-degree orbiting position), refrigerant gas is introduced into an inner suction chamber A1 through the inlet port 43 and the through-hole 52 of the circular vane 51, and compression is performed in an outer compression chamber B2 while the outer compression chamber B2 does not communicate with the inlet port 43 and the outer outlet port 44a. Refrigerant gas is compressed in an inner compression chamber A2, and at the same time, the compressed refrigerant gas is discharged out of the inner compression chamber A2 through the inner outlet port 44.
At the 90-degree orbiting position of the orbiting vane 5 of the compression unit P, the compression is still performed in the outer compression chamber B2, and almost all the compressed refrigerant gas is discharged out of the inner compression chamber A2 through the inner outlet port 44. At this stage, an outer suction chamber B1 appears so that refrigerant gas is introduced into the outer suction chamber B1 through the inlet port 43.
At the 180-degree orbiting position of the orbiting vane 5 of the compression unit P, the inner suction chamber A1 disappears. Specifically, the inner suction chamber A1 is changed into the inner compression chamber A2, and therefore, compression is performed in the inner compression chamber A2. At this stage, the outer compression chamber B2 communicates with the outer outlet port 44a. Consequently, compressed refrigerant gas is discharged out of the outer compression chamber B2 through the outer outlet port 44a. 
At the 270-degree orbiting position of the orbiting vane 5 of the compression unit P, almost all the compressed refrigerant gas is discharged out of the outer compression chamber B2 through the outer outlet port 44a, and the compression is still performed in the inner compression chamber A2. Also, compression is newly performed in the outer suction chamber B1. When the orbiting vane 5 of the compression unit P further performs the orbiting movement by 90 degrees, the outer suction chamber B1 disappears. Specifically, the outer suction chamber B1 is changed into the outer compression chamber B2, and therefore, the compression is continuously performed in the outer compression chamber B2. As a result, the orbiting vane 5 of the compression unit P is returned to the position where the orbiting movement of the orbiting vane 5 is initiated. In this way, a 360-degree-per-cycle orbiting movement of the orbiting vane 5 of the compression unit P is accomplished. The orbiting movement of the orbiting vane 5 of the compression unit P is performed in a continuous fashion.
The slider 54 is slidably disposed in the opening 53 for maintaining the seal between the inner and outer compression chambers A2 and B2.
In the conventional orbiting vane compressor with the above-stated construction, however, excessive upward axial force, i.e., excessive axial lifting force is applied to the orbiting vane due to high-pressure refrigerant gas introduced to the lower surface of the vane plate of the orbiting vane. As a result, interference occurs between the upper surface of the orbiting vane and the inner surface of the cylinder, and therefore, excessive friction occurs between the orbiting vane and the cylinder.
The excessive friction between the orbiting vane and the cylinder causes frictional loss during the orbiting movement of the orbiting vane. Consequently, performance of the orbiting vane compressor is deteriorated.